1. Field of the Invention
The present invention relates to an endoscope having a wide viewing angle and a suction channel for suctioning waste materials or the like in a body cavity such as large intestine, and a front cover.
2. Description of the Related Art
Conventionally, endoscopes are used widely in the medical field or the like. For example, a long and narrow insertion portion of an endoscope is inserted into a body cavity, so that organs or the like in the body cavity can be observed, and various treatments can be given by using treatment instruments which are inserted into a treatment instrument insertion channel as the need arises. A distal end of the insertion portion is provided with a bendable portion, and an operation portion of the endoscope is operated so that an observing direction of an observation window at the distal end can be changed.
A viewing angle of conventional endoscopes is about 120 to 140°, and an operator observes a body cavity by means of an observing image at its viewing angle. However, when the operator desires to observe a portion which is out of the visual field range while observing the body cavity, the operator curves the bendable portion so as to observe the portion which is out of visual field range.
On the other hand, an endoscope whose viewing angle is further widened in order to observe a wider range is also proposed (for example, Japanese Patent Application Laid-Open No. 2001-258823).
Japanese Patent Application Laid-Open No. 2001-258823 discloses an endoscope where an observation optical system having a wide viewing angle of about 140° to 210° is disposed at a distal end portion. In the document, according to the widening of the angle of the observation optical system, an illumination optical system which is disposed at the distal end portion and illuminates a body cavity is disposed so that its optical axis is overlapped with the optical axis of the observation optical system which tilts at a predetermined angle in order to illuminate an entire observation portion in the body cavity. That is, the distal end portion of the endoscope insertion portion is formed into a so-called cannon shape where a distal end surface through which the optical axis of the observation optical system passes is the most distal end, and the surface of the illumination optical system is disposed on the tapered surface. Further, the distal end surface of the endoscope insertion portion serves also as the treatment instrument insertion channel, and has an opening of a suction channel for suctioning waste materials, mucous membrane and the like in the body cavity such as large intestine.